During the formation of hydronium ion, water molecule acts as donor.

Coordinate covalent bond is represented by an arrow from donor to acceptor.

Compounds having coordinate covalent bonds are $CO, HNO _3, NH _4^+$.

Addition of acid to water results in the formation of $H _3O^+$.

Covalent compunds are soft(due to presence of cloud of electrons between the bonding atoms), have low melting point(due to weak forces of attraction) and are bad conductors of electricity in the molten state(due to lack of free electrons)

The 2 electrons of an atom( generally lone pair) is donated by one atom to the other atom and it results in the formation of a coordinate bond.

A hydronium ion is written as ${ H } _{ 3 }{ O }^{ + }$. 

I , II and III statement about covalent compounds are correct but the IV one is not correct since the aqueous solution of the covalent compound do not contain free ions and thus are not the good conductors of electricity .

$ H _3O^+$ will have three bond pairs and one lone pair and shape same as $NH _3$ is therefore pyramidal. The hydroxonium ion is isoelectronic with ammonia and has an identical shape of pyramidal. 

When ammonium is formed, the fourth hydrogen is formed is attached by dative covalent bond because the only hydrogen nucleus is transferred from chlorine to nitrogen. The hydrogen electron left behind on the chlorine to form the negative chloride ion.

Covalent compounds are very resistant, they do not conduct heat and electricity, mostly insulators. They have low boiling points as they are gases at room temperature. It is very hard to molten the covalent compounds because of high bond energy. Therefore the covalent compound turns liquid from solid state easily. They show low melting points and are non polar hence insoluble in water.

When there is back bonding from central to side atom change in hybridization takes place. Back bonding takes place when one atom has vacant orbital and one has lone pairs. 
So central atom has a lone pair and side atom must have vacant orbital 
So : $CCl^- _3$
$N (SiH _3) _3$
$Sp^3 - Sp^2$

Carbon monoxide and nitric oxide contains dative bond or coordinate covalent bond whereas carbon dioxide and dichlorine monoxide contains covalent bonds.

Hetrolytic bond dissociation of $HCN$:
$H-CN\rightarrow H^++ ^-C\equiv N$.
So here, negative charge is on $C$.

Both the electrons of a coordinate bond are donated by one atom, and then shared by both the atoms of the bond.

In potassium ferrocyanide, iron atom has vacant orbitals and cyanide ions have unpaired electrons. Hence, in potassium ferrocyanide, the bond between iron and cyanide ions is dative bond.

The bond formed between $P{H} _{3}$ and ${H}^{+}$ is dative covalent bond in which the bonding electrons are coming from phosphine.

Coordinate covalent components have la slight dipole moment. So they are less solube in nonpolar solvents compared to polar solvents.

$CuSO _4\cdot 5H _2O$ exists as $[Cu(H _2O) _4]^{2+} SO _{4}^{2-}\cdot H _2O$.
It has dative bonds in $[Cu(H _2O) _4]^{2+}$, which is between water molecules and Cu. There is an ionic bond between the coordination sphere and $SO _4^{2-}$ ion. Covalent bond between S and O in  in $SO _4^{2-}$ ions and between H and O in water molecules Within the molecules of $H _2O$, there is hydrogen bonding. 

In $NH _4^+$ the $N$ forms a co-ordinate covalent bond with one $H$ by utilizing the lone pair of electrons.

Ammonium ions are formed by transfer of a hydrogen ion from HCl to the lone pair of electrons on the ammonia molecule.

The electronegativity difference between the two atoms is $3.0 - 1.2 = 1.8$. It is large, hence, the bond formed is an ionic bond. The more electronegative atom gains one or more electrons to form an anion and the less electronegative atom loses one or more electrons to form a cation. 

A co-ordinate or dative bond is a covalent bond(a shared pair of electrons) in which both the electrons come from the same atom. It is shown by an arrow and the arrow points from atom donating the lone pair to accepting atom.$\quad \quad H\ \quad \quad \quad |\ H-{ N }^{ + }\rightarrow H\ \quad \quad \quad |\ \quad \quad H$

A covalent bond is formed between sulfur and oxygen as they both are non metals and the bond between copper and sulfate is ionic one is metal and other non metal. Hydrated coppersulfate is a complex which is bonded to water molecules acting as ligands forming coordinate bond.

A coordination compound is a metal atom or ion bonded by covalent bonds to ligands. For example, tetra carbonyl nickel $\displaystyle  Ni(CO) _4$ is a coordination compound with the metal atom ($Ni$ atom) which forms covalent bonds with $4$ $CO$ ligands.

The molecules already having positive charge $(Na^+ $ and $ H _3O^+) $ means that they are electron deficient and they can not combine with another proton $(H^+)$. $HCl$ is an acid, that releases a proton. Ammonia $NH _3$ acts as a base because, the unshared pair of electrons in the ammonia molecule can combine with a proton, forming the ammonium $(NH _4^+)$ ion. 

Assertion: The weakest of the forces between molecules are dispersion forces or London forces.
Reason: Dispersion forces or London forces represent the weak attractive forces that originate as a result of instantaneous dipoles induced in atoms or molecules.
Hence, both the assertion and reason are not correct.

In a dative bond, the shared pair of electrons come from the same atom. In $NH _{4}^{+}$ all the 4 valence electrons of N are bonded to the hydrogen atoms, thus it cannot act as an electron pair donor for the formation of dative bond.

The unique thing about the bonds in coordination compounds is that one of the atoms or ions donates both shared electrons. Thus, the bond is covalent coordinate bond.

Dative bond is present in the $\displaystyle PCl _5$ molecule.
In the solid state, $\displaystyle PCl _5$ molecule exists in the form of $\displaystyle [PCl _4]^+$ $\displaystyle [PCl _6]^-$
Dative bond is present in $\displaystyle [PCl _6]^-$ ion. The chloride ion is the donor atom and P atom is acceptor atom. The dative bond is also called co ordinate covalent bond.

A coordinate covalent bond is represented by an single arrow from donor to acceptor.
A coordinate bond is formed when one atom donates its pair of electrons to the other atom. For example, a lone pair of electrons on N atom of ammonia is donated to a proton to form ammonium ion with a coordinate bond between N and H.

 (A) $\displaystyle NH _4^+$ ion contains a dative bond (co-ordinate covalent bond) between $\displaystyle N$ atom and  $\displaystyle H$ atom.
$\displaystyle H _3N \rightarrow H^+$

(B) Bond angle increases when a bond is formed between $\displaystyle NH _3$ and $\displaystyle H^+$. In $\displaystyle NH _3$ molecule, due to repulsion between lone pair and bond pair of electrons, the bond angle decreases. When $\displaystyle NH _4^+$ ion is formed, lone pair is converted into bond pair. The inter electron repulsion decreases and bond angle increases.

(C) $\displaystyle NH _4^+$ ion has tetrahedral shape. $\displaystyle NH _3$ molecule has pyramidal shape.

(D) The type of hybridisation is not changed when bond is formed between $\displaystyle NH _3$ and $\displaystyle H^+$

$\displaystyle  NH^+ _4$  and $\displaystyle  H _3O^+$  have coordinate covalent bonds.
$\displaystyle  NH^+ _4$ is formed by a coordinate covalent bond between $\displaystyle  NH _3$  and $\displaystyle  H^+$.
$\displaystyle  H _3O^+$ is formed by a coordinate covalent bond between $\displaystyle  H _2O$  and $\displaystyle  H^+$. 

$\displaystyle {N} _{2}{H} _{3}^{+}$ contain a coordinate covalent bond.
$\displaystyle H-N=\underset{\displaystyle \underset{\displaystyle H}{\downarrow}}{N}^+-H$
The N atom is the donor atom and H atom is the acceptor atom.

The bonds present in  $\displaystyle K _4 [Fe(CN) _6]$ are ionic, covalent and coordinate covalent bonds. Ionic bonds are present between $\displaystyle K^+$ ion and $\displaystyle [Fe(CN) _6]^{4-}$ ion.
Covalent bonds are present in $\displaystyle C \equiv N$ ligand.
Co-ordinate covalent bonds are present between $\displaystyle Fe$ and $\displaystyle C$ and also in between $\displaystyle C$ and $\displaystyle N$.

In $\displaystyle ammonium $ ion $\displaystyle NH _4^+$ three $\displaystyle N-H$ bonds are covalent and one $\displaystyle N-H$ bond is coordinate covalent (dative). $Hydrogen$ atoms are situated at the corners of a tetrahedron as $\displaystyle N$ atom is $\displaystyle sp^3$ hybridised.

From the given compounds only Hydronium ion forms a coordinate or dative bond, where $O$ is the donor atom and $H$ is the acceptor.

Coordinate covalent bond is a special type of covalent bond in which only one of the bonded atoms contributes the electron pair for sharing.

No. of covalent bonds and coordinate bonds.

Coordinate bond is formed between electron rich and electron deficient atoms. The donor atom should have at least one lone pair of electrons and the acceptor atom should have at least one vacant orbital.

$NH _3$ forms coordinate  bond with the Hydronium ion.

As the valence shell of $H$ atom has single electron and it forms single sigma bond with itself.

$H _{2}SO _{4}$  has $3$ types of bonds- ionic, covalent and coordinate. Sulphur is the central atom,surrounded by $4$ oxygen atoms and $2$ hydrogen atoms places on left of any $2$ oxygen atoms. Now, oxygen shares one electron each with the sulphur and hydrogen atom. But by this only $2$ oxygen atoms will be able to complete octet. The remaining $2$ will complete by coordinate bonding. Both the oxygen atoms will take electrons from sulphur but sulphur won't take theirs ie sharing from only one end. This is called coordinate bond. Hydronium ions are attached with sulphate ions using ionic bonding
${ K } _{ 4 }[{ Fe(CN) } _{ 6 }]\ $: has ionic bond between ${ K }^{ + }and  { [{ Fe(CN) } _{ 6 }] }^{ 4- }$, coordinate bonding in $CN$ and covalent bond in ${ [{ Fe(CN) } _{ 6 }] }^{ 4- }$
$\ { NH } _{ 4 }Cl\ $: has ionic bond between $\ { { NH } _{ 4 } }^{ + }and  { Cl }^{ -}$, coordinate bonding in $\ { { NH } _{ 4 } }^{ + }$ and covalent bond in $\ { { NH } _{ 3 } .}^{  }\quad \$

${ N } _{ 2 }{ H } _{ 5 }^{ + }$ is formed from ${ N } _{ 2 }{ H } _{ 4 }$ which has a lone pair of electrons on $'N'$ and positive charge on $'H'$ takes away its electron and to complete duplet, a co-ordinate bond is present from $N$ to $H$.